A peculiar technique of partial invocation that summons only an organ: the oesophagus of a great, fire-breathing toad from Mount Myōboku: Rock Lodging (妙木山・岩宿, Myōbokuzan: Iwayado), the user sends themselves and the enemy into the toad's stomach. If activated inside a building or a cave, this trick can ensnare the enemy without them realising it. In this interior, even the foothold is unreliable, the enemy finds themselves in a tight spot, having a hard time performing at their usual level of skill, and unable to find a proper response. The inside of the oesophagus is highly flexible, and adhesive, and won't even allow liberty of movement. In time, the walls of flesh close in and envelop the enemy, dooming them to go inside the stomach where they will be digested.

Jiraiya could control the oesophagus, causing it to expand, contract, or grow in whatever direction he wished, even making his walls act defensively, enveloping the target he wants to protect, like Jiraya did with Sasuke. When first used, Jiraiya claimed that no one had ever escaped from this technique. Itachi Uchiha and Kisame Hoshigaki managed to escape when Itachi used Amaterasu to burn through the oesophagus, which is said to be fire-resistant.

Trivia

In the video games, parts of the oesophagus also spew fire, which fits with Jiraiya's description of the animal the toad oesophagus originates from.

'Gamaguchi' (蝦蟇口, Literally meaning: toad mouth) is a Japanese name for a pouch or wallet, especially one closed with a metal clasp and used for small change. Naruto's own wallet is a reference to this word as well.[1]